1. Field of the Invention
The invention relates to a device and method for deciding characteristics of a differential signal cable and, in particular, to a device and method for deciding characteristics of a differential signal cable which is used for high-speed differential signal transmission at a transmission rate of not less than 10 G baud.
2. Description of the Related Art
High-speed differential signal transmission at not less than 10 G baud is performed for communication between servers and switches in data centers, or for inter-device communication or in-device communication of high-performance computing (HPC) systems. In comparison with conventional differential signal cables used for transmitting differential signals at several G baud, differential signal cables used for transmitting high-speed differential signals at not less than 10 G baud have a trouble to transmit signals even with slight variation in transmission characteristics. The variation in transmission characteristics is caused by e.g., fine dust attached to a connector portion or bending of cable with an extremely small radius of curvature due to mishandling etc.
When transmitting high-speed differential signals at not less than 10 G baud, communication failure may occur due to variation in transmission characteristics of differential signal cable as well as due to, e.g., a malfunction of a transmitting or receiving circuit, inadequate setting of the transmitting or receiving circuit, design and manufacturing conditions (transmission loss, signaling rate, characteristics of via stub, etc.) of a printed circuit board connecting the transmitting and receiving circuits to the cable, or inappropriate insertion/removal of connector, etc. Furthermore, communication failure also may occur due to indirect causes such as the cooling state of the device or unstable power supply.
In the high-speed differential signal transmission at not less than 10 G baud, signals equalization is generally performed by a transmitter-side circuit or a receiver-side circuit to shape the signal waveform and the optimal setting values of equalizer parameters are different depending on frequency characteristics of transmission components. The optimal setting values of equalizer parameters are often determined by auto setting algorithm of the transmitting and receiving circuits. However, the auto setting may fail since optimization of the auto setting algorithm is not necessarily designed for the differential signal cable.
For such reasons, it is difficult to identify the cause of communication failure, particularly difficult to detect a malfunction of a differential signal cable when the differential signal cable is used for high-speed differential signal transmission at not less than 10 G baud. Based on this fact, devices and methods for inspecting differential signal cables have been examined, and one of which is, e.g., a method in which a pseudo random signal is send and received to measure a bit error rate (see JP-A-2013-046283).